1. Field of the Invention
The present invention relates to an ophthalmic photographing apparatus and more particularly to an exposure control therefore. More specifically, the present invention pertains to an exposure control system for an ophthalmic photographing apparatus wherein the exposure is determined so that a desired extent of exposure is established at a desired part of an ophthalmic subject to be photographed.
2. Description of Prior Art
In a conventional ophthalmic photographic instrument, for example, an eye fundus camera, the exposure for photographing is generally determined by detecting an overall quantity of light reflected at the retina of a patient's eye by means, for example a CdS detector. In other words, the exposure is determined in accordance with an average quantity of light beams from various parts of the eye retina. It should however be noted that the retina is constituted by various parts of different reflectivities, such as a disk, a network of blood vessels, a yellow spot, and the like so that the picture taken under the exposure determined as described above usually includes portions of under-exposure as well as portions of over-exposure. This very often causes serious problems in photographing diseased eyes because precise photographic records of diseased portions are particularly critical for determining curative treatment.